Tuning indicator tube



Aug. 18, 1936.

H. M. WAGNER I 2,051,189

TUNING INDICATOR TUBE 7 Filed June 27, 1935 INVENTOR HERBERT M. WAGNER ATTORNEY Patented Aug. 18, 1936 TUNING INDICATOR TUBE .Herbert M. Wagner, Newark. N. .L, assignor, by

mesne assignments, to Radio Corporation of America, New York, N. Y.,. a corporation of Delaware Application June 27, 1935, Serial No. 28,689

7 Claims;

My invention relates to electron discharge devices, more particularly to such devices useful as visual indicators of voltage and having a fluorescent electrode which is rendered luminous and has the appearance of a pattern of light, which may be of constant width and varying length and which changes in response to the change in the magnitude of the applied voltage, a device of this character being particularly useful as a tuning indicator in radio receiving sets. The present invention is an improvement over a device of the general character described and claimed in.

a' copending application of Harry C. Thompson, Serial No. 28,665, filed June 27, 1935 and assigned 16 to the same assignee as the present invention.

It is an object of my invention to provide an electron discharge device of this general character which is particularly suitable for use as a tuning indicator in a radio receiving set in which resonance is indicated by. a brilliant luminous glow on the anode, and in which departure from resonance is. indicated by a dark space or gap between edges of a luminous pattern of light.

One embodiment of such a device useful as a tuning indicator and described in the Thompson application referred to above comprises an 'envelope having within it a straight thermionic equipotential cathode provided with two separate emitting sections, one of which is surrounded by amplifier elements which may comprise a control grid and anode, and the other of which is surrounded by the tuning indicator elements of the tube consisting of a straight control electrode parallel to the cathode and an anode coated with fluorescent material which may be concentric mum width, the dark portion of minimum width,

when the circuit is tuned to resonance, and pref- 5o erably the entire anode is made-fluorescent and the dark portion disappears.- 1

The novel features which I believe to be characteristic of my invention are set forth with par-' ticularity in the appendedclaims, but the invention itself will best be understood by reference (Cl. 250-215) V I v to the following description taken in connection with the accompanying drawing in which Figure 1 shows an electron discharge device-embodying my invention with parts broken away to show details of construction; Figures 2 and 3 are top 5 ViLWS with parts removed toshow the tuning indicator portion of the tube and the'pattern of light under difierent voltage conditions; .Fig-

ures 4 and 5 are top views of modifications of the tuning indicator shown in Figures 2 and 3; 10 Figure 6 is a perspective view of another modification of the electrode construction of the tuning indicator section of a tube made in accordance with my invention; Figure 7 is a circuit diagram embodying a tuning indicator tube madein ate-. cordance with my invention. The electron discharge device or tuning indicator tube shown in Figure 1 comprises an evacuated envelope 10 provided with the usual stem upper end of the mount. The cathode I3 is ex- 30 tended upwardly and provided with a second emitting section 16 adjacent which is placed the control electrode H which may be a rod or a vane shaped from sheet material and placed edgewise to the cathode. This control electrode I1 35 is supported from and connected to one of the side rods of the anode I5. Surrounding and concentric with the emitting portion I6"of the cathodeis an anode l9 shaped like a dishpan having a collar 20 and a coating 2| fluorescent under 40 electron bombardment. The electrons emitted fromv the cathode and striking the anode with sufiicient'velocity, cause it to fluoresce.- A cap 22 is positioned over the top end of the cathode ,fbest shown in Figure 6. The cap 22 also serves as an electrostatic shield to.-pre'vent any stray charges that might develop on the glass envelope 5 from aflecting the electron beamfrom the bathode to the fluorescent anode.

In this type of tuning indicator the electrons;

travel radially outward from the cathode to the fluorescent coating on the anode in a wide beam. The extent ofthe surface of the anode reached by the electron beam is determined by the voltage on-the control electrode IT. The less negative this electrodeis with respect-to the anode 20, that is'the more positive with respect to the,,cathode 16, the greater: the area of the anode covered by the -beam and the greater the area of the fluorescent portion of the anode. According to my invention, the control electrode I! is at a positive potentialwith respect tothe cathode. The advantages of this are that the boundaries of the electron beam are sharp and well defined, there coupled directly to an amplifier.

can'be a high concentration of electrons at the edges of the luminous areas of the anode so that the edges are'brighter and stand out more prominently, a high current to the luminescent anode and hence high luminosity is obtained with low anode voltages, and the control electrode can be I have found also that a tube made in accordance with my invention is not critical to variations in cathode temperature, and that it can also be used witheither alternating or direct voltages and currents.

,The tube is viewed from the end-so that the pattern of light is viewed as shown in Figures 2' and 3. As shown in Figure 2 when the control electrode is at a potential near that of the cathode the anode fiuoresces only over the area indicated by the shaded lines. As the electrode beare used instead of one, two separate luminescent portions being obtained. In this arrangement the pattern of light extends around the entire circumference of the anode 20 when the circuit in which the tube is used is tuned to resonance; By

depending upon the dark space to indicate voltage conditions, several advantages areobtainedover tubes depending only on the width or length of a luminous indication. The range of indication can be made all the way from zero dark space to a maximum gap between bright areas of considerable width thru which thebeain edges can move. It is also possible to extend the rarme by making the control electrode so positive that overlapping of the electnon beam-results. .Where beams overlap the luminosity is increased greatly so that at the overlapping portion the luminosity is very intense. The fluorescent surface of the anode can, therefore, be used more than once so that the range is extended; that is, it can be used once for the gap and again for the overlap. The most important advantage obtained, however, is that the eye is very sensitive to changes in beam width in the neighborhood of zero width; that is, where the beam edges just touch. As a res lt the tuning of a set in which the tuning indi'cator tube is used, can be made very precise.

In the modification shown in Figure 6 the con- .trol electrode 24 of sheet metal mounted ed'gewise to the cathode is formed to taper from the top made in accordance with my invention.

minescent areas can begiven shapes other than straight lines. V v

In Figure 7, I show a circuit embodying a'tube The anode l5 of the triode section and the' anode i9 of the tuning indicator section are electrically connected to each other thru a resistor 25. The

fluorescentanode is connected directly toa source of voltage supply 25. When no current. flows from cathode I3 there is no voltage drop in resistor 25 and the anode l5 and control electrode H, which is connected to it, are at substantially the same potential as the anode I9 01 the tuning ure 2, or when two control electrodes are used a.

pattern such as shown in Figure 4. The magni-v tude of the current, thru the triode portion of the tube is determined by the bias on the control grid l4.

In the circuit shown, a diode detector or rectifier 21 has its anode 28 and its cathode 29 connected to opposite sides of the secondary of the intermediate or radio frequency transformer 32 tuned by condenser 36, thecathode being connected thru the resistor 30 and by-pass condenser 3|. The cathode side of the transformer 32 is connected" to the control grid l4 thru resistor 33. the grid being by-passed by means of by -pass condenser 24 so that a bias is impressed on the v grid IA. The conductor 35 may be connected to the automatic volume control circuit. In the arrangement shown with the set untuned and no signal passing thru the transformer 32, no current passes thru resistor 30 and no bias is developed. The grid I4 is at ground potential and permits current to flow thru the triode section of the tube under which conditions the control electrode I1 is at a potential near that of the cathode as described above, the light pattern takes,

the form shown in Figure 2. With the set tuned to a signal a rectified current passes thru resistor 30 developing a drop across t resistor and impressing a bias on the control grid H of the triode thru-the resistor 33. This reduces the current passing thru the tri'ode in proportion to thebias impressed upon the grid so that the control electrode l'l becomes more positive with respect to ments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I- claim as new is- -l. Anelectron discharge device having an envelope, a cathode within said envelope for emitting electrons, a dish-shaped anode surrounding said cathode and having its interior surface coated with a fluorescent material for receiving electrons from said cathode to produce a luminous annular shaped pattern .on said anode, a control electrode positioned between said anode and said '1 cathode and parallel to the cathode for determining the area of the fluorescent surface of the anode reached by the electrons from said cathode.-

2. An electron discharge device having an envelope, a cathode within said envelope for emitting electrons, a dish shaped anode surrounding said cathode and having its interior surface coated with'a fluorescent material for receiving electrons from said cathode to produce a pattern of light, a straight rod-like control electrode between said cathode and said'anode and parallel to the cathode, and a cup-shaped member positioned over the end of said cathode and cooperating with said dish-shaped member to confine the electrons from said cathode to the surface of said anode.

3. An electr'on discharge device having an envelope, a cathode within said envelope for emitting electrons, a dish-shaped anode surrounding said cathode and provided with a fluorescent coating for receiving electrons from said cathode, a cup-shaped member positioned over the end of said cathodeand electrically connected to said dish-shaped anode for confining the electrons from the cathode to the surface of the anode, and a control electrode positioned between said cath-' ode and anode and comprising a straight rod-like member parallel to the cathode for determinin that portion of the surface of the anode reached by electrons from the cathode to cause the anode to fluoresce.

4. An electrondischarge device having an envelope, a straight thermionic cathode within said envelope having two separate emitting sections thereon, a grid and anode surrounding one of said emitting sections and a control electrode adjacent the other emitting section electrically connected to and supported by said anode, anda second 5 anode concentric with and positioned around said other emitting section of the cathode and said a control electrode and having a fluorescent coating on the interior thereof, and a cap positioned over one end of said cathode and electrically connected 10 to the coated anode.

5. An electron discharge device having an envelope, a straight thermionic cathode within said envelope having two separate emitting sections thereon, a grid and an anode surrounding one of 1 said emitting sections and a control electrode adjacent the other emittingsectlon electrically connected to and supported by said anode, and a second anode concentric with and positioned around said other emitting section of the cathode and 20 said control electrode, and having a fluorescent coating on the interior surface thereof.

6. An electron discharge device having an envelope, a cathode within said envelope'for emitting electrons, a dish-shaped anode surrounding said cathode and having its interior surface coated'with a fluorescent material for receiving electrons from said cathode toproduce a luminous annular shaped pattern on said anode, a control electrode positioned between said anode and said 30 cathode and parallel to theeathode for producing a dark space on the fluorescent surface of said anode, the size of which changes in response to changes in the voltage applied to said control electrode. 3

'1. An electron discharge device having an envelope,-a cathode within said envelope for emitting electrons, a dish-shaped anode surrounding said cathode and having its interior surface coated with a fluorescent material for receiving electrons from said cathode to produce a pattern of light on said anode, a straight rod-like control elec- .trode between said cathode and said anode and parallel to the cathode for producing a dark space on the pattern of light on the surface of the anode which changes in response to changes in voltages applied to said control electrode and a cup-shaped member positioned over the end of said cathode and cooperating with said dish-shaped member to confine the electrons from said cathode to the 50 surface of said anode.

T H. WAGNER. 

